This invention relates to the prestressing of concrete, and more particularly to a prestressing apparatus of the type having two cylinder-piston units, the pistons being connected to one another via their piston rods by a first arm, and the cylinders being connected to one another by a second arm.
Prestressing apparatus is used in the building industry for prestressing reinforcement cables or strands of reinforcement cable in recesses or shafts of structures. Prior art trunk-piston prestressing apparatus frequently requires too long a recess or shaft. Furthermore, so-called tandem or twin-piston apparatus having two adjacent cylinder-piston units with parallel axes have been proposed, both the piston rods and cylinders of these units being connected by yokes, and the units being hydraulically connected in parallel. The output of force takes place via the two yokes in the middle axis between the two cylinder-piston units. However, such prestressing apparatus cannot be used for tensioning a large number wires or strands disposed closely side by side. The space required in the width of the recess would be too great with such apparatus.